According to a reply from CE customers are not allowed to post images on Facebook because FB's terms contradict the RF license. The explanation is: uploading to FB grants the right to sub-licensing of content and the customer has no such right.

I understand from IS customer support that visitlondon has bought a standard licence and the image was put on their facebook cover page in high res.

Since when is the buyer a redistributor and copyright holder of our images?

I don't see any response from anyone in Contributor Relations quite yet so I'm not sure who you talked to. Regardless, your contact ticket is assigned to the right department. They will get to your concern in due course. If you have any additional question feel free to contact me via site mail.